Adhesive preparations containing a drug are widely used. Since synthetic rubbers used as an adhesive do not have a functional group, they are advantageous in that the contained drug shows good stability. However, since such synthetic rubbers show low drug solubility, when a drug is contained in an adhesive layer, separation of the drug from the adhesive layer becomes a problem. For example, the following reference deals with problems relating to the dissolution of a drug in an adhesive layer.
JP-A-2006-76994 discloses an adhesive preparation containing two kinds of polyisobutylene having different molecular weights, fentanyl (drug), and fatty acid alkyl ester and long chain branched alcohol (organic liquid components).
This reference teaches that the proportion of the drug relative to the total weight of an adhesive layer is preferably not more than 2.5 wt %. This is because when a large amount of a drug is added to an adhesive layer of this kind of adhesive preparation, the drug may be separated from the adhesive layer, and this problem is yet to be improved.
To suppress separation of a drug from an adhesive layer, an organic liquid component may be added as a dissolution agent to an adhesive layer. However, when a large amount of an organic liquid component is added to an adhesive layer, the cohesion strength of the adhesive layer may decrease, and oozing during preservation of the adhesive preparation and adhesive residue on the skin upon peeling off of the adhesive preparation from the skin may be developed. In fact, this reference describes that when a proportion of an organic liquid component relative to the total weight of an adhesive layer exceeds 20%, the cohesion strength of the adhesive layer decreases markedly and a cohesive failure easily occurs. As described above, the aforementioned reference suggests difficulty associated with a large amount of an organic liquid component in an adhesive layer of such an adhesive preparation.
As is clear from the above, an adhesive preparation wherein a drug is sufficiently dissolved in an adhesive layer and is not easily separated from the adhesive layer even during preservation of the adhesive preparation has not been known.